In previous studies on immune response in mice infected with M. leprae, attempts were made to evaluate the humoral response. As a parallel to these studies, the cell-mediated immune response in similarly infected mice was evaluated, with the idea of placing the mouse model in the spectrum of human leprosy. Identical studies were carried out with mice infected with M. lepraemurium and M. marinum. The studies on M. leprae infected mice indicated that the mouse model can be placed in the BB or BT spectrum of human leprosy whereas the studies on M. lapraemurium infected mice indicated an immune response similar to that exhibited by patients in advanced stages of leprosy infection. The M. marinum studies have shown that this model is not the most convenient one to be used as a parallel for such studies with M. leprae infected mouse model. Studies on the antigenic mosaic of acid-fast bacilli isolated from human leproma, have shown no similarity between these organisms and M. leprae. Isoelectric focusing, a highly sensitive separation technique, have yielded fractions from M. smegmatis CF and CE, that appear to have single antigens. Similar studies are in progress on the M. leprae CE and other mycobacterial preparations. The aims of proposed studies are as follows: 1. Attempts will be made to use the newly employed isoelectric focusing method of separation either singly or in combination with other chromatographic methods, for further separation and purification of the M. leprae antigens. These antigens will be evaluated in terms of their abilities to elicit and/or induce hypersensitivity and to confer immunity. 2. Efforts will be made to separate the antigens, both shared and unshared, of other mycobacterial species, and to evaluate their potential to confer immunity against M. leprae infection in mice.